Antimicrobial size emulsion and gypsum panel made therewith

ABSTRACT

Disclosed is an emulsion of an internal paper size and a biocidal emulsifying agent, such as a cationic non-starchy quaternary ammonium compounds, that is introduced into a paper-making furnish to produce an antimicrobial paper. The antimicrobial paper is useful as facing for gypsum panels. A method of making the paper includes emulsifying the internal size with a biocide before introducing the size to the paper furnish. A method of making a microbial growth resistant gypsum panel that incorporates the antimicrobial paper is also disclosed.

RELATED APPLICATION

This application claims priority pursuant to 35 U.S.C. 119(e) from U.S.Provisional Application Ser. No. 61/428,080 filed Dec. 29, 2010.

FIELD OF THE INVENTION

This invention relates to an emulsion of an alkenylsuccinic anhydridepaper size (“ASA”) or an alkyl ketene dimer (“AKD”) paper size and abiocide whereby the biocide has a dual function as a biocide and anemulsifying agent.

BACKGROUND

Gypsum boards, also known as gypsum panels, drywall and wallboards, arepopular construction materials with desirable properties for indoorapplications. They are durable, economical and fire-retardant. Inaddition, these boards provide excellent compressive strength propertiesand a relatively low density. They are easily decorated and areattractive as surfaces, especially for interior construction.

Manufacturing of gypsum boards includes forming a slurry of calciumsulfate hemihydrate, water and additives and continuously depositing theslurry on a conveyor belt or a forming table. Often, a paper coversheet, also known as a facer, moves on the conveyor beneath a mixer tocontinuously deposit slurry on the facer. Often, a second paper coversheet, or facer, is applied over the slurry. The resultant assembly isformed into the shape of a panel. Calcium sulfate hemihydrate reactswith water in the slurry, converting the hemihydrate into a matrix ofinterlocking calcium sulfate dihydrate crystals, causing the slurry toset and become firm. This forms a continuous strip of hardened materialhaving, optionally, no cover sheets, a front and back cover sheet, orjust one cover sheet on either the front or back of the panel. Thecontinuous strip moves on the conveyor until the calcined gypsum issufficiently set to withstand handling and movement from the conveyor toanother place, such as a kiln, and the strip is thereafter cut to formboards of desired length. Water that is in excess of the amount neededfor hydration of the calcined gypsum is removed from the gypsum panel ina kiln.

Gypsum panel manufacturers often use a biocide to protect the panelsfrom attack by microorganisms such as mold and fungi by treating thepaper coverings. However, treated paper alone is often insufficient tocontrol mold growth for a number of reasons. Many biocides lose efficacythrough the drying process in the kiln due to the high temperatures. Thebiocide can be overwhelmed by large quantities of mold spores that areincorporated into the gypsum and paper from water used during the panelforming process, combined with spores from the air. In some cases, perenvironmental regulations, there is a limit to the concentration ofbiocide that can be present on the surface of the paper. It appears thatthe maximum allowable biocide concentration is not sufficient to protectboth the paper and the set gypsum core in all cases.

Microbial growth favors environments where spores find moisture andnutrients to metabolize. Temperature is also a factor, but numerousspecies of microorganisms thrive at the temperatures required for humanhabitation, where gypsum boards are most often used. Therefore,opportunities to control microbial growth consist mostly of controllingavailability of moisture and nutrients. It is desirable to have amechanism for killing microorganisms that begin to grow in or on agypsum panel or a facer. Water vapor and spores are unavoidable inenvironments where gypsum panels are used, even though gypsum board isnormally used in interior construction. In addition to moisture that ispresent in the environment, products used in interior constructionsometimes encounter water due to seepage, leaky roofs or pipes,flooding, condensation, and the like. These exposures occur without anydefects in the gypsum board manufacture or use. It is accepted that onceexposed to moisture, traditional gypsum panel products are susceptibleto microbial growth.

Starch is an example of a nutrient that microorganisms thrive on. Ingypsum panels, starch is frequently used for a number of purposes. Itmay be added to a calcined gypsum slurry to promote adhesion between thecore and the facer. Often a facer is made of paper, and starch may be acomponent of the paper commonly used to cover gypsum panels. Starch(sugar) coated particles of calcium sulfate dihydrate are often used asa set accelerator in a calcined gypsum slurry. Other starches may alsobe used to modify different properties of the set gypsum composition.When starches are present in the cover materials or the gypsum cores ofgypsum panels, there is sufficient nutrition for possible microbialgrowth once the spores come into contact with the nutritious medium ofthe farinaceous panel.

Cover sheets for gypsum panels, also known as facers, facing material,paper facers, etc., are made by a paper manufacturing processes thatbegins with preparation of a dilute pulp of fibers, chemical additivesand water. The pulp is drained through a screen to form a mat ofrandomly intertwined fibers. Additional water is removed by pressing themat or applying suction. Informally, the “wet end” refers to thepaper-making process before water removal, and the stage of the processafter excess water is removed is called the “dry end.” Additives, suchas size, may be added during either or both of these stages.

Paper size is a hydrophobic compound that improves a paper's strengthand its resistance to penetration by liquids such as water and ink.Alkyl ketene dimer (“AKD”) and alkenylsuccinic anhydride (“ASA”), bothof which are hydrophobic, are common sizing agents. Rosin and rosinderivatives are another class of paper sizing agents known in the paperindustry. For good sizing efficiency, the size is applied as very smallparticles. This, and the hydrophobic property, requires that ASA and/orAKD be emulsified in an aqueous solution in order to properly introduceand anchor the sizing to the paper's fibers. Internal size isincorporated into the paper itself during the wet end of themanufacturing process. External size is applied to the surface of thefinished paper product by dry end coating processes such as dipping,spraying or rolling.

ASA internal size is usually prepared on-site at a paper plant byemulsion with a cationic starch stabilizer as described in U.S. Pat. No.6,159,339, herein incorporated by reference. A high charge, lowmolecular weight polymer may also be used as an emulsifier of theinternal paper size in water. Alternatively, an AKD emulsion may beprepared by first dispersing a starch phosphate derivative in the waterwhich is to become the continuous phase of the emulsion. Then, AKD isadded and thoroughly admixed at temperatures from about 140° F.-160° F.until a smooth, homogeneous emulsion is attained. High shear mixingequipment is used to agitate the ketene dimmer and aqueous starchphosphate mixture to attain the desired emulsion.

Disadvantages associated with known AKD emulsification practices aretypically overcome by emulsifying the AKD off-site and supplying it topaper manufacturers as a fully formulated emulsion. Emulsifying AKD is adifficult process that ordinarily requires expensive and highlyspecialized equipment. For the purpose of stabilizing AKD emulsions,additives such as surfactants and protective colloids may be present inthe emulsion composition. The AKD may react with some of theseadditives, thereby reducing the efficiency of the size by reducing theamount of active ingredient that is available. Anionic surfactantspresent in an AKD emulsion further reduce efficiency of the size becausethe cellulosic material to which the size is expected to anchor is alsoanionic, thereby repelling the size particles rather than favoringintroduction of the size to the cellulosic fibers. Another disadvantageof the typical AKD emulsion supply is economic because it is expensiveto transport the large amounts of water that are part of the AKDemulsion to the paper manufacturer.

ASA emulsions are unstable, with a maximum shelf life between 6 and 8hours depending on the make down water pH and temperature. Typically,the ASA emulsion is stored for 30 minutes prior to use. It is desirableto keep the ASA oil very dry and to wait until the last possible momentto prepare the aqueous emulsion. Frequently, paper-makers prepare thedesired amount of ASA emulsion 30 minutes before the solution is addedto the furnish. Cationic starch emulsifiers utilized in preparation ofthe aqueous ASA size emulsions provide a cationic starch sheath aroundeach ASA droplet, anchoring the size to the anionic cellulosic paperfibers. It is still possible for much of the ASA to flow from the fiberswith the process water. This gives the ASA time to decompose byhydrolysis, impairing the ASA sizing efficiency, causing deposit to formon the paper machine, higher operating costs and paper quality issues.Complicated and expensive wet end chemistry is often needed to achievesatisfactory retention of the size. Dry end testing, such as highperformance liquid chromatography (“HPLC”) is common to ensure thatretention of the ASA size is satisfactory and that it is consistent.

Prior art attempts to reduce microbial growth on gypsum boards includereplacing paper facings with fiberglass-based facings, eliminating asource of starch nutrition and deterring microorganisms from growing onthe board surfaces. Attempts to make gypsum boards resistant tomicrobial growth have also been made by incorporation of a biocide, suchas a salt of pyrithione, into the core, the facers, or both, as revealedin U.S. Pat. No. 6,893,752 entitled “Mold Resistant Gypsum Panel andMethod of Making Same,” herein incorporated by reference.

Quaternary ammonium compounds are loosely defined as a class ofcompounds generally having the formula R₁R₂R₃R₄—N⁺Y⁻, where the radicalsmay be the same, different or part of a ring and Y is a counter anion.Typically, but not always, one of the radicals is a long-chain alkylgroup. Certain quaternary ammonium compounds possess biocidalproperties. Prior art teaches the use of biocidal quaternary ammoniumcompounds in the gypsum core, or as a surface coating of paper facers,whether applied by spraying, dipping, rolling or any other dry endcoating method.

While quaternary ammonium compounds are appreciated for their ability tocontrol the growth of microorganisms, they are often avoided inpaper-making because they produce foam, even at low concentrations. Foamhas detrimental effects on the quality of the final paper product byforming pin-holes, circular marks on the paper, lower paper strength andreduced production. Often, the solution to foam problems involvescomplicated wet end chemistry to prevent foam formation with anti-foamcompounds or to de-foam the paper furnish with de-foaming compounds.Another method of controlling foam in aqueous solutions of quaternaryammonium compounds is by adding anionic surfactants to the solution, asdisclosed in International Publication Number WO 2008/049616 entitled“Controlled Foam Aqueous Quaternary Ammonium And PhosphoniumCompositions,” herein incorporated by reference. As noted in thispublication, the biocidal efficacy of quaternary ammonium compounds iscompromised by addition of the anionic surfactant.

There is an ongoing need for gypsum board products that offer reducedsusceptibility to microbial growth without compromising their beneficialproperties. In addition, there is an ongoing need for commerciallyviable manufacturing methods for such products. There also remains aneed for improvement in the efficiency and workability of AKD and ASApaper size as well as an improvement in retention of biocide compoundsused in paper-making.

SUMMARY OF THE INVENTION

One or more of these needs is met by the present invention, whichfeatures a biocidal sizing emulsion of a size and a biocidal emulsifyingagent in water. The biocidal sizing emulsion is used to make a biocidalpaper for use on a gypsum panel. Yet another embodiment is a biocidalgypsum panel with a paper facer that includes the biocidal sizingemulsion.

Surprisingly, the paper with beneficial properties provided by both asize and a biocide can be made without separate emulsifying agents andbiocidal compounds. Biocidal emulsifying agents have been found,unexpectedly, to emulsify an internal paper size for addition to afurnish of a paper-making manufacturing process. Efficiencies and costsavings in the paper-making process are introduced due to the dualfunction of the biocide.

As a result of being able to use the biocidal emulsifying agent as aninternal paper size emulsifier, the final paper product is made strongerand more durable. Strength is achieved by improving resistance to fluidsthrough effective sizing. Durability is achieved by improving resistanceto microorganisms.

Compared to prior art internal paper size emulsions utilizingemulsifying agents that combine a starch, a polymer and a surfactant,the claimed biocidal sizing emulsion contributes to improving theefficiency of the paper-making process. This is due to the fact that onecompound, the biocide, is taking the place of several chemicaladditives. No starch, polymer or surfactant is required, yet the sizedpaper made with the biocidal sizing emulsion also has the beneficialproperty of being resistant to growth of microorganisms without additionof an additive that is separate from the size emulsifying agent.

Also, when a non-starchy, cationic quaternary ammonium compound isselected as the biocidal emulsifying agent, an additional surprisingimprovement in the paper-making process efficiency is realized. Foam,which is usually associated with utilizing quaternary ammonium compoundsin a paper furnish, is reduced or is severely destabilized. Neither ananti-foaming nor a de-foaming agent is required to control the foam.Thus, efficiency associated with utilizing one compound to accomplishthree functions previously known to require at least three separatecompounds, is attributed to the biocidal emulsifying agent used in thebiocidal sizing emulsion.

The biocidal emulsifying agent used in the biocidal sizing emulsion iscationic, providing good retention in the paper sheet, reducing the needfor complicated wet-end retention chemistry. Dry end quality controltesting for adequate and consistent biocide dosing is also minimized.These improvements in the paper-making process are expected to result inless complex, less expensive and more consistent procedures and resultsof manufacturing of paper facers and the gypsum panels that the paperfacers cover.

An ASA emulsion utilizing the biocidal emulsifying agent remains stablelonger, improving manufacturing efficiency and workability of the ASApaper size. It is contemplated that a biocidal sizing emulsion made withAKD can also be made at a paper-mill or a gypsum manufacturing plant,thereby reducing the expense of transporting pre-emulsified AKD and thelarge quantity of water associated with it.

Another important feature of this invention is that a biocidal gypsumpanel can be made without resorting to fiberglass or otherless-desirable, non-paper facers. It is also an improvement to providefor more biocide in the paper cover sheet, which is a paper ply closerto the surface of the gypsum panel, where most of the mold, mildew, orfungus defacement problem is most likely to accrue.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a biocidal sizing emulsion where onephase is an internal paper sizing agent and a biocidal emulsifyingagent. The second, continuous phase is water. No other biocide oremulsifying agent need be present in the biocidal sizing emulsion ofthis invention. The biocidal sizing emulsion may be utilized inmanufacturing of paper facers for gypsum boards. The biocidal sizingemulsion provides an improved method of manufacture that is moreefficient and commercially viable, as well as an improved product withthe biocidal emulsifying agent that is better retained in a product,such as a paper facer.

Compounds referred to herein as “biocidal emulsifying agents” arelimited to biocides which emulsify internal paper size and become partof the finished paper product so that anti-microbial properties areimparted to the paper product. A biocidal additive (“biocide”) to paperis effective in reducing microorganism growth on wallboard panels andtheir facers. The terms microbe, bacteria, mold, mildew and fungus areused interchangeably to refer to the many microorganisms that couldpotentially grow on these surfaces.

Preferred internal sizing agents are alkenyl succinic anhydride (“ASA”)and alkyl ketene dimmer (“AKD”). The ASA internal size is an oily liquidat room temperature. It is stored where it can remain dry, as it is veryunstable. It will react with water or water vapor to hydrolyze andbecome unusable as an internal sizing agent. An example of the ASA sizethat is effective in this invention is Bubond 650. (BuckmanLaboratories, Memphis, Tenn.). Also, Prequel® 1000/Prequel® 630 (AshlandHercules, Wilmington, Del.) and Nalco® 7548/Nalco® 7540 (Nalco,Naperville, Ill.) are additional examples of the ASA size.

In one embodiment, a biocidal sizing emulsion of the internal paper sizeis made with the biocidal emulsifying agent and water. Preferably, ASAinternal paper size is emulsified with a biocidal emulsifying agent thatis a non-starchy cationic quaternary ammonium compound. Morespecifically, quaternary ammonium compounds useful in this biocidalsizing emulsion are alkyl dimethyl benzyl ammonium chloride (ADBAC),alkyl dimethyl ethyl benzyl ammonium chloride (EBC), dialkyl dimethylammonium chloride, didecyl dimethyl ammonium chloride, and combinationsthereof. In another embodiment, the non-starchy cationic biocide is oneor a combination of dequalinium chloride, didecyl-dimethylphosphoniumchloride, didodecyl-ethyl-isobutylphosphonium, adihexyldecyl-ethyl-isobutylphosphonium, a long chain alkyl amine, aguanidine, a bis(3-aminopropyl)dodecylamine, polyaminopropyl biguanideor iodopropynyl butylcarbamate. When one of these biocidal emulsifyingagents is selected to emulsify the internal paper size, no additionalemulsifying agent is required. Polymers, surfactants, starches, andother compounds known to emulsify or stabilize ASA and AKD can beeliminated.

Emulsification of the internal size provides small droplets to allow forefficient anchoring of the size to the paper pulp fibers. The ASA sizeis a hydrophobic, oily liquid that is typically 100% solids. Thebiocidal emulsifying agent is typically 20% to 80% solids and is firstdiluted with primary water in a static mixer. The amount of the primarywater used for dilution of the biocidal emulsifying agent isapproximately 10% of the total emulsification process water requirementfor a 40% solids biocide. Little or no water may be required when abiocidal emulsifying agent is lower in solids than 40%. A stream ofdiluted biocidal emulsifying agent is combined with a stream of 100%solids ASA, and the resultant solution is pumped through a turbine pumpat a differential pressure between 200-230 psi to make a biocidal sizingemulsion. Droplets in the biocidal sizing emulsion range in size from0.5 microns to 1.5 microns in diameter. The stream of the biocidalsizing emulsion is further diluted with secondary water. The solids ofthe emulsified ASA can be adjusted to a concentration of approximately1% and pumped into a paper-making furnish. Depending on operatingconditions, the final solids concentration of the emulsified ASA may beadjusted lower or higher than 1%; but once the emulsification dilutionwater is determined for a particular paper machine it need not beadjusted.

The amount of biocidal emulsifying agent utilized in the biocidal sizingemulsion is directly related to the amount of biocide needed to controlmicroorganism growth and the amount needed to emulsify the size. Paperswith different compositions are made for application in differentenvironments, thus the antimicrobial requirement can increase ordecrease depending on the likelihood that there will be sufficientnutrition, moisture and other factors that promote growth ofmicroorganisms. Likewise, the size may call for different amounts ofemulsifying agent depending on the quantity of size required to achievesufficient protection from fluids for the paper being made. Thisacceptable dosage or concentration of biocidal emulsifying agent willthen be used to emulsify the ASA and checked for particle size, foamingand emulsion stability.

A size dosage is determined by evaluating the water resistance needed toproduce the grade or type of paper. Generally, these grades are higherin water resistance because both mold and water resistance is requiredfor these grades. The ratio of the internal size, also known as a sizingagent, to the biocidal emulsifying agent is preferably one part size toone part biocidal emulsifying agent. The ratio may range from 1:1 to1:0.5 size to biocidal emulsifying agent. The quantity of size varies,but is generally between 2 lb/ton to 20 lb/ton of air dried paper; ormore typically between 5 lb/ton to 10 lb/ton. For example, a 5000 ppmASA emulsified size will contain 41.2% biocide emulsifying agent, or2060 ppm, and the remaining material is ASA size.

In Example 2, below, a method of selecting a concentration of biocidalemulsifying agent is demonstrated. For example, the 2060 ppm of biocidalemulsifying agent described above must show no mold growth aftertreating a standard 1% CMC solution with 0.25% ASA size mixture.

It is contemplated that the AKD internal size would be an alternativeand workable substitute for the ASA in the biocidal sizing emulsion ofthis invention. The AKD biocidal sizing emulsions could be made at thepaper-mill or gypsum panel manufacturing plan thereby reducing theexpense of transporting the pre-emulsified AKD and the large quantity ofwater associated with it. Further, it is contemplated that a surfactantor polymer may be utilized with the biocidal sizing emulsion of thepresent invention. One embodiment includes utilization of a non-anionicsurfactant or polymer in the biocidal sizing emulsion.

Emulsifying an ASA or AKD sizing agent with a biocidal emulsifying agentis accomplished by utilizing known emulsification methods. No changes tostandard equipment are required, but small changes in flow rates orturbine back pressures may occur to produce the biocidal sizing emulsionof suitable quality, i.e. particle size, distribution and stability.

An exemplary method utilized for emulsifying ASA size in the laboratoryis described. First, tare a Senor mini blender cup and add 1 gram of ASAsize to the cup. Then add 0.7 grams of the biocidal emulsifying agent tothe cup with the ASA size and add enough water to make a 100 grambiocidal sizing emulsion with the above two ingredients. Place the Senorcup on a blender and turn the blender on high for 90 seconds. A 100 gramquantity of ASA size is ready to treat a dilute suspension of paperfibers. If needed, the emulsifier ratio can be adjusted depending onsolids and the quality of the emulsion.

In another embodiment, a sized multi-ply paper is produced. There areoptionally two emulsifying units to minimize any paper manufacturingequipment down time. One or more paper plies are made with the biocidalemulsifying agent and size blend to prevent mold and a secondemulsifying agent may be used to produce a sized paper under normalemulsification procedures. This reduces the sizing cost and allows thebiocide to treat just the outer paper plies which are exposed to moldspores. The biocidal sizing emulsion is optionally added to the paperfurnish by adding it to the suction side of a fan pump, but could beadded on the pump pressure side.

Selection of the biocidal emulsifying agent for the paper making processutilizes the same criteria that applies to selection of the biocidalemulsifying agent for the biocidal sizing emulsion. There is a balanceof how much water to add and final dilution in the paper machine. Asmore water is added, the size is better dispersed and it becomes moreuniformly distributed. However, additional water adds additional expensebecause the water is typically softened. This may change the waterbalance of the paper making process, causing the plant to discharge someprocess water.

The biocidal sizing emulsion at 1% solids is stored in a small tank thatwill turnover every 30 to 60 minutes to minimize hydrolysis. The size ispumped to the fan pump using a centrifuge at low pressure, 20 to 25 psi.Adding the sizing solution to a paper furnish by measuring theconsistency, flow rate of the fibers and the percent solids, as well asthe flow rate of the dilute size, the paper-making process can becompleted on any conventional paper-making machine. Often, paper facersare made with several plies or layers. Sometimes, as few as two pliesare used. Other times, as many as seven or more plies are utilized.Paper additives or size may be added to the paper furnish through a headbox or before a refiner, but are normally added to the fan pump thatfeeds the dilute furnish to a headbox.

Yet another embodiment of this invention utilizes the above-describedemulsion and paper in a method of making a mold-resistant gypsum panelthat includes selecting the biocidal emulsifying agent, emulsifying theASA or AKD internal sizing agent with the biocidal emulsifying agent toform the biocidal sizing emulsion, adding the biocidal sizing emulsionto the paper furnish that will be processed to form the paper facer uponwhich a gypsum slurry will be placed and set to form a gypsum panel orboard. Paper facers are often manufactured by gypsum board manufacturersas part of the gypsum board manufacturing process.

Preparing a slurry of calcium sulfate hemihydrate and water is madeaccording to conventional gypsum slurry methods. Calcium sulfatehemihydrate and water in excess of the amount needed to rehydrate thecalcium sulfate hemihydrate are mixed to form a flowable slurry.Additives such as starch, foam, accelerator, dispersing agent, etc. arecontemplated as part of the gypsum slurry. There are no adverse ordesirable interactions between the additives and the biocidal paperfacer.

The antimicrobial paper facer that is made with the furnish enhanced bythe biocidal sizing emulsion is made to roll along a forming table on aconveyor belt. The gypsum slurry is continuously deposited onto thefacer. As the paper and slurry traverse the conveyor, a second paperfacer may be placed onto the top surface of the gypsum slurry before itsets. Setting of gypsum slurry involves an exothermic reaction wherebywater is taken up by the calcium sulfate hemihydrate and gypsum crystalsare formed. As more and more crystallization takes place, the slurrybecomes more and more solid. Setting progress is measured by the rise intemperature of the slurry. In a gypsum board manufacturing plant, it isuseful to take the temperature of the material on the conveyor at thepoint where it is to be cut by a knife into the desired size boardpieces. The finished gypsum board is microbe-resistant as a result ofhaving at least one antimicrobial paper facing. It is contemplated thata biocidal emulsifying agent may be added to the gypsum slurry, andtherefore be present in the gypsum core as well.

The following examples are meant to further explain and illustrate theinvention. The Examples are not intended to limit the scope of theinvention.

EXAMPLE 1

Laboratory paper handsheets were produced with various internal sizeemulsions. The sheets showed excellent resistance to water absorption,as well as good resistance to microorganism growth. Size emulsions forthe paper sheets were made with NALCO® 7540 ASA size, manufactured inNaperville, Ill. The size was combined with each of the antimicrobialcomponents in Tables I and II in a 10:1 weight ratio of ASA size tobiocidal emulsifying agent.

The biocidal emulsifying agents were quaternary ammonium chloridecompounds that were obtained from Mason Chemical Company in Joliet, Ill.MAQUAT® MC1416 and MAQUAT® MC1412 were both 80% active alkyl dimethylbenzyl ammonium chloride (ADBAC) compounds. MAQUAT® MQ2525 was an 80%active combination of alkyl dimethyl benzyl ammonium chloride and alkyldimethyl ethyl benzyl ammonium chloride. MAQUAT® MQ624M was received asan 80% active biocidal emulsifying agent , but was diluted and utilizedin the laboratory as a 45% active combination of alkyl dimethyl benzylammonium chloride and dialkyl dimethyl ammonium chloride. MAQUAT® 4480E,didecyl dimethyl ammonium chloride, was similarly diluted from 80% to45% biocidally active compound.

Four gram, two-ply hand sheets were made in a laboratory procedure thatutilized a British laboratory hand sheet mold. 100% old corrugatedcontainer (“OCC”) furnish was pulverized to make a fibrous pulp.Biocidal sizing emulsions of ASA in the various biocides shown in TableI were made by adding an aqueous solution of the biocidal emulsifyingagent with the size, according to the Laboratory Method of EmulsifyingASA Size set forth above, to achieve properly sized droplets ofemulsified ASA. This aqueous biocidal sizing emulsion was furtherdiluted with additional water to obtain a 1% or low dilution of ASA sizeand biocidal emulsifying agent. The paper furnish slurry of pulp, waterand emulsified size was then pressed in an Adirondack roll press at 20psi and the resultant sheets were dried in a laboratory drum dryer at240° F. for 2.5 minutes.

These hand sheets were then tested for water and mold resistance. Thewater resistance tests included a TAPPI T441 Standard Cobb Test, hereinincorporated by reference, and a Boiling Boat Test, which measures howlong (up to 1,000 seconds) it takes for boiling water to soak through50% of the paper sheet. The Cobb Test was operated at 120° F. for 3minutes.

The Boiling Boat Test included floating a piece of paper on boilingwater to determine the degree of water repellency. Paper samples wereprepared by cutting 12″×12″ pieces of paper to be tested. The papersample was placed bond-side (bond-side is the side that is attached tothe gypsum panel) down on a flat surface. A 6″×6″ jig, or a solid, flatobject, was placed directly in the center of the piece of paper. Withthe jig as an aid, creases along each edge of the jig and across thecorners were made to form a three-dimensional boat-like structure out ofthe piece of paper. One corner of the paper sample was folded up andover to an adjacent side, then stapled in place. Two staples in eachcorner worked well. This folding and stapling was repeated for each sideto make the boat and hold the paper in the boat formation. A 4′×4′rubber stamp was used to make an impression of a grid in the center (oras close as possible to the center) of the bottom of the paper boat.

An aluminum or stainless steel tray, measuring 10″ square and 3″ deep,was placed on a hot plate that was at least 10″ square. The tray wasfilled approximately ⅔ full of water, a thermometer was put into thewater, and the hot plate heat was turned to “high.” When the waterreached 97° C.±3° C., the paper boat was placed into the water whilestarting a stopwatch. When the paper or a portion of the paper becamewet it was observable as a darkening of the wet area. The measurablearea in the grid on the bottom of the boat that was darkened wasmeasured after 5 and 15 minutes, provided the paper did not reach 50%wetted. The test was stopped when 50% (12-13 squares of the grid) waswetted or after 15 minutes (1,000 seconds).

To measure the wetness of the bottom of the boat, the number of gridsquares that were wetted through was counted. Estimates to the nearest ¼square were made. The number of squares was multiplied by 4 to determinethe percent of wetting.

Table I shows Cobb and Boiling Boat test results for size efficacy ofASA size in various biocidal sizing emulsions. Both sets of test resultsindicate very good sizing of the paper. No polymer was included in thesesamples, labeled with letter and number codes from B1 to F3. Sample Awas a control with no biocidal emulsifying agent and only ASA internalsize and a polymer (NALCO® 7541) emulsifying agent.

Table II shows Cobb and Boiling Boat test results for size efficacy ofASA size in NALCO® 7541 polymer emulsions. Comparison of the Cobb andBoiling Boat test results shows very good sizing in all samples. Thisconclusion was supported by the fact that it took more than 1,000seconds (17 minutes) to wet 50% of the paper in the Boiling Boat Test.The Cobb Test results were also very good. It was surprising that ASAinternal size was just as effective when emulsified with a biocidalemulsifying agent as it was when emulsified, according to standardpractice, with a polymer.

TABLE I Poly- Cobb Boiling Size mer Biocide g/ Boat Code Biocide #/ton#/ton #/ton 100 cm² seconds A Control (none) 10 7 0 0.49 1000+ B1 MAQUATMC 1416 10 0 1 0.51 1000+ B2 MAQUAT MC 1416 20 0 2 0.56 1000+ B3 MAQUATMC 1416 30 0 3 0.48 1000+ C1 MAQUAT MC1412 10 0 1 0.49 1000+ C2 MAQUATMC1412 20 0 2 0.52 1000+ C3 MAQUAT MC1412 30 0 3 0.51 1000+ D1 MAQUATMQ2525 10 0 1 0.54 1000+ D2 MAQUAT MQ2525 20 0 2 0.53 1000+ D3 MAQUATMQ2525 30 0 3 0.49 1000+ E1 MAQUAT MQ624M 10 0 1 0.65 1000+ (modified)E2 MAQUAT MQ624M 20 0 2 0.58 1000+ (modified) E3 MAQUAT MQ624M 30 0 30.55 1000+ (modified) F1 MAQUAT 4480E 10 0 1 0.63 1000+ F2 MAQUAT 4480E20 0 2 0.66 1000+ F3 MAQUAT 4480E 30 0 3 0.57 1000+

TABLE II Cobb Boiling Size Polymer Biocide g/ Boat Code Biocide #/ton#/ton #/ton 100 cm² seconds G1 FUNGITROL 10 7 1 0.62 1000+ 920-20% G2FUNGITROL 20 7 2 0.58 1000+ 920-20% G3 FUNGITROL 30 7 3 0.60 1000+920-20% H1 FUNGITROL 11- 10 7 1 0.57 1000+ 100% H2 FUNGITROL 11- 20 7 20.62 1000+ 100% H3 FUNGITROL 11- 30 7 3 0.63 1000+ 100%

All samples, A-H3, shown in Tables I and II, plus another control werealso subjected to a modified ASTM G21 Fungal Defacement Test. Thecontrol ensured that the test would grow mold and the sizing performancewould be similar to the control. Two, one square inch, paper sampleswere cut form each handsheet and were placed on solidified nutrient-saltagars in a Petri dish so each paper side was tested. The Petri withpaper samples dish were incubated at 28-30° C. with a relative humiditygreater than 85% for a period of time before it was observed. The papersamples were wetted with sterile water and contain only the mold sporesfrom the air.

At 7 and 14 days the front and the back of the paper sheet samples wereinspected for surface microbial growth. The results are shown in TableIV. A value of “0” indicates no microbial growth on the sample surface.A value of “1” indicates 1-10% growth; “2” indicates 11-30% growth; “3”indicates 31-60% growth; and “4” indicates greater than 61% growth. Theratings of the paper samples in Table IV are shown in Table III asfollows:

TABLE III Minimum Maximum ASTM G- Time Time 21 USG General Frame GrowthFrame Growth Rating Rating Less than Shows  7 days Shows 3 to 4 Notfungus 7 days growth growth resistant 7 days No growth 14 days Shows 3to 4 Not fungus growth resistant 7 days No growth 14 days Sparse 0 to 2Moderately growth fungus resistant 7 days none 14 days None 0 Fungusresistant

TABLE IV SAMPLE 7 DAYS 7 DAYS 14 DAYS 14 DAYS CODE Front Back Front BackA 0 4 4 4 B1 1 3 4 4 B2 1 0 2 1 B3 2 1 4 4 C1 4 4 4 4 C2 1 4 4 4 C3 2 14 4 D1 1 4 4 4 D2 1 0 4 1 D3 4 4 4 4 E1 2 0 4 4 E2 0 1 4 4 E3 4 4 4 4 F10 2 4 4 F2 4 4 4 4 F3 4 4 4 4 CONTROL 4 4 4 4

The sample codes in Table IV refer to the same sample codes in Tables Iand II. Sample A was a control. Biocidal effect is observed in sampleswith biocidal emulsifying agent added. It is contemplated thatincreasing the concentration of biocidal emulsifying agent will improvethe antimicrobial performance of the paper.

EXAMPLE 2

The biocidal size emulsion was utilized in a method of making amold-resistant paper facer that included selecting a biocidalemulsifying agent. One method of selecting a concentration of a singularor a blend of several biocidal emulsifying agents was to complete aseries of dilutions of the components prior to emulsifying the ASA ortreating the paper. A medium to low molecular weight carboxyl methylcellulose (“CMC”), an emulsion stabilizer, at 1% and 0.25% ASA size wasblended in a beaker as a standard solution. Five milliliters of thisstandard solution was pipetted into eight different sterile test tubes.The test biocidal emulsifying agent was diluted to make a 2.5% solution.See Table V.

TABLE V Biocide CMC + Sterile Spores Test Conc ASA Size Water 10,000Biocide Total Tube (ppm) (ml) (ml) cfu 2.5% (ml) 1 0 5.0 4.8 0.2 0 10 210,000 5.0 0.8 0.2 4.0 10 3 5,000 5.0 2.8 0.2 2.0 10 4 2,500 5.0 3.8 0.21.0 10 5 1,250 5.0 4.3 0.2 0.5 10 6 625 5.0 4.55 0.2 0.25 10 7 312 5.04.67 0.2 0.13 10 8 156 5.0 4.74 0.2 0.06 10

A 1 ml aliquot was placed in a petri dish and observed after 3, 5 or 7days. The mold colonies were counted on each Petri dish to obtain nofungal colonies at the lowest biocidal emulsifying agent concentration.After these tests were completed a standard handsheet was made using thebiocide to emulsify the ASA size. Sizing performance was evaluated,paper properties were measured and ASTM G21 fungal testing was completedon the paper.

It is contemplated that greater quantities of biocidal emulsifying agentwould improve the microorganism resistance without compromising thesizing or other properties of the paper product.

While particular embodiments of the biocidal size emulsification, thebiocidal paper facer and the biocidal gypsum panel have been shown anddescribed, it will be appreciated by those skilled in the art thatchanges and modifications may be made thereto without departing from theinvention in its broader aspects and as set forth in the followingclaims.

What is claimed is:
 1. A biocidal sizing emulsion comprising: aninternal sizing agent; and a biocidal emulsifying agent, wherein thebiocidal emulsifying agent is a non-starchy quaternary ammoniumcompound, and wherein the internal sizing agent and biocidal emulsifyingagent are emulsified in water.
 2. The biocidal sizing emulsion of claim1 wherein said emulsion is free of an additional emulsifying agent. 3.The biocidal sizing emulsion of claim 1 wherein said biocidalemulsifying agent is a non-starchy cationic quaternary ammoniumcompound.
 4. The biocidal sizing emulsion of claim 1 wherein saidinternal sizing agent is selected from the group consisting of alkenylsuccinic anhydride and alkyl ketene dimer.
 5. The biocidal sizingemulsion of claim 1 wherein said quaternary ammonium compound is atleast one selected from the group consisting of alkyl dimethyl benzylammonium chloride, alkyl dimethyl ethyl benzyl ammonium chloride,dialkyl dimethyl ammonium chloride, didecyl dimethyl ammonium chloride,and combinations thereof.
 6. The biocidal sizing emulsion of claim 1wherein said internal sizing agent is alkenyl succinic anhydride.
 7. Thebiocidal sizing emulsion of claim 1 wherein said biocidal emulsifyingagent is selected from the group consisting of dequalinium chloride,didecyl-dimethylphosphonium chloride,didadecyl-ethyl-isobutylphosphonium,dihexyldecyl-ethyl-isobutylphosphonium, long chain alkyl amines,guanidines, bis(3-aminopropyl) dodecylamine and polyaminopropylbiguanide, or a combination thereof.
 8. The biocidal sizing emulsion ofclaim 1 wherein the ratio of the internal sizing agent to the biocidalemulsifying agent is one part ASA size and half to one part biocidalemulsifying agent.